1. Field of the Invention
The present inventions relate to apparatus and methods for drying materials, and, more particularly, to apparatus and methods for pulse combustion drying.
2. Background of the Related Art
The typical pulse combustion dryer includes a combustor connected to a tailpipe. The combustor defines a combustion chamber. Fuel and air may be admitted into the combustion chamber through an air inlet and fuel inlet, respectively, and the resulting fuel-air mixture periodically ignited to propel pulses of heated combustion products through the tailpipe from the combustion chamber. The term “pulse combustion” thus originates from the periodic ignition of solid, liquid, or gaseous fuel to generate pulses of heated combustion products, in contrast to the continuous ignition of fuel in conventional dryers. The material to be dried may be introduced into the pulses of heated combustion products typically in the tailpipe and/or in a drying chamber in fluid communication with the tailpipe.
Some pulse combustion dryers may include a mechanical valve such as a reed valve, flapper valve, or rotary valve to provide a physical barrier to prevent backflow of heated combustion products through the air inlet. However, mechanical valves may be mechanically complex, may require maintenance, and may be prone to failure due to, for example, mechanical stresses, thermal stresses, fatigue, and corrosion by the heated combustion products. Rotary valves may require a feed back control system to synchronize the rotation of the rotary valve with the frequency of the combustion cycle.
A fluid diode may also be used to control flow through the air inlet of the pulse combustion dryer. The fluid diode generally allows airflow relatively freely through the air inlet into the combustion chamber, and generally prevents backflow of heated combustion products from the combustion chamber through the air inlet. This flow direction asymmetry is achieved without moving parts, which may avoid some of the problems associated with mechanical valves. However, pulse combustion dryers that use fluid diodes to control backflow of heated combustion products through the air inlet may still experience some backflow of heated combustion products through the air inlet.
Accordingly, a need exists for improved pulse combustion dryers that may avoid the shortcomings noted above.